Process for brominated styrenic polymers

ABSTRACT

This invention relates to the bromination of styrenic polymers by contacting same with a brominating agent in the presence of a bromination catalyst and, as a reaction solvent, bromochloromethane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 08/721,389 filedSep. 26, 1996, now abandoned, which application is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to the discovery of a highly beneficial solventfor use in the bromination of a styrenic polymer.

Brominated styrenic polymers, e.g., brominated polystyrene, are wellrecognized flame retardants for use in engineering thermoplastics, e.g.,nylon, polyethylene terephthalate, polybutylene terephthalate, etc.These flame retardants are prepared by reacting a brominating agent,e.g., bromine or bromine chloride, with a polystyrene in the presence ofa Lewis acid catalyst. Since the styrenic polymer is usually veryviscous or a solid, it has been deemed necessary to provide it to thereaction as a solute in a lower viscosity solution. The art generallydescribes the solvent as being a halogenated hydrocarbon, and, morespecifically, a chlorinated hydrocarbon. Methylene chloride anddichloroethane are universally considered to be the solvents of choice.Despite their apparent attractiveness, these two solvents are notwithout disadvantage.

Methylene chloride is favored as it is relatively inert in the process.However, it is disadvantaged because it has a low boiling point and ischallenged as being potentially depletive of the global ozone layer.

In distinction, dichloroethane has an acceptable boiling point and, inuse, is more environmentally desirable than methylene chloride. It isnot, however, a panacea as it reacts in the process to a significantextent and its use is not associated with an exceptionably low colorbrominated polystyrene product.

It is, therefore, an object of this invention to provide a solvent foruse in the bromination of styrenic polymers which is environmentallybeneficial, has a boiling point in the range of 80°-95° C., isrelatively inert in the bromination process, and is associated with anear-white brominated styrenic polymer product.

The Invention

This invention relates to a process for brominating styrenic polymers,which process comprises: brominating styrenic polymer in the presence ofLewis acid catalyst and solvent quantities of bromochloromethane.

The bromination of the styrenic polymer is preferably effected by either(1) adding a brominating agent to a reactor containing styrenic polymer,bromochloromethane and a Lewis acid catalyst; (2) adding, to a Lewisacid catalyst, (i) a styrenic polymer stream which is comprised of asolution of styrenic polymer and bromochloromethane and (ii) abrominating agent stream, the streams being added separately butsubstantially concurrently; or (3) adding a mixture which includes abrominating agent, styrenic polymer and bromochloromethane to a Lewisacid catalyst. Besides these preferred modes of addition, it iscontemplated that any addition mode which effects reactive contactbetween the brominating agent, catalyst and styrenic polymer will bebenefited by the use of bromochloromethane as the process solvent. Thefirst-described addition mode is conventional and is illustrated in U.S.Pat. No. 4,200,703 and U.S. Pat. No. 4,352,909. Both of these patentsare incorporated herein by reference for all of their teachings exceptfor that teaching which refers to the identity of the process solvent.(Thus, in the '703 patent, column 3, lines 3-16, the Examples and theClaims are excluded, while in the '909 patent, the paragraph bridgingcolumns 7 and 8, the Examples and the Claims are also excluded.) Thesecond-described addition mode is illustrated by U.S. Pat. No. 4,975,496which is also incorporated herein by reference for all of its teachingsexcept for that teaching which refers to the process solvent.

For addition mode (2), it is a feature that there be a dispersion of atleast a portion of the brominating agent substantially throughout thecatalyst before there is any substantial complexing (cross-linking) ofthe styrenic polymer. When the brominating catalyst is AlCl₃, there isgenerally a need to pre-add a portion of the bromine to the catalystprior to introduction of the styrenic polymer. In such cases, at least 5mole percent of the brominating agent is pre-added. See incorporatedU.S. Pat. No. 4,975,496 for further details concerning the pre-additionof the brominating agent.

For mode (3), it is preferred that the mixture be formed via mixing ofthe components in a device which is outside or inside of the reactor andfeeding the resultant mix to the reactor. In addition, a stream from thereactor can also be fed to the mixing device to contribute to the totalresultant mix being sent back to the reactor. Also, for addition mode(3), it is preferred that the bromochloromethane, styrenic polymer andthe brominating agent be substantially free of brominating catalyst atleast prior to their being mixed. The phrase, "substantially free of abromination catalyst", is to be taken to mean less than a catalyticallyeffective amount of catalyst. With such low amounts, little or nocatalyzed bromination or cross-linking should occur. Generally, suchamounts will be less than 500 ppm (weight basis) of styrenic polymerpresent.

The amount of bromochloromethane solvent used is that amount which candissolve the styrenic polymer and any of the brominated styrenic polymerspecies produced. Also, it is preferred that the amount ofbromochloromethane used will result in an easily-stirred reaction mass.Generally, the total solvent used will be that amount which is needed todissolve the styrenic polymer to yield an easy-flowing solution and thatamount which may be initially present in the reactor and associated withreaction components other than styrenic polymer. In most cases, theamount of bromochloromethane used to form the styrenic polymer solutionwill provide a solution which contains 3 to 30 wt % styrenic polymer,based upon the total weight of the solution.

The presence or absence of water in the bromochloromethane will be inaccordance with the water requirements of the particular process chosen.For example, anhydrous processes, such as that described in U.S. Pat.No. 4,352,909, will be sensitive to the solvent water content. Otherprocesses, such as that disclosed in U.S. Pat. No. 4,200,702, require acertain level of water and, thus, are not as sensitive to the solventwater content. Still other processes, which are substantiallyindependent of water content, can be somewhat indifferent about thesolvent water content. Unless the solvent is being used as a majorcontributor of water to the process, most practitioners will choosebromochloromethane having less than about 100 ppm (weight basis) water.

Preferred Embodiments

Styrenic polymers which are brominated in accordance with the presentinvention are homopolymers and copolymers of vinyl aromatic monomers,that is, monomers having an unsaturated moiety and an aromatic moiety.The preferred vinyl aromatic monomers have the formula:

    H.sub.2 C═CR--Ar

wherein R is hydrogen or an alkyl group having from 1 to 4 carbon atomsand Ar is an aromatic radical (including various alkyl andhalo-ring-substituted aromatic units) of from 6 to 10 carbon atoms.Examples of such vinyl aromatic monomers are styrene,alpha-methylstyrene, orthomethylstyrene, meta-methylstyrene,para-methylstyrene, para-ethylstyrene, isopropenyltoluene,isopropenylnaphthalene, vinyl toluene, vinyl naphthalene, vinylbiphenyl, vinyl anthracene, the dimethylstyrenes, t-butylstyrene, theseveral chlorostyrenes (such as the mono- and dichloro-variants), theseveral bromostyrenes (such as the mono-, dibromo- and tribromo-variants). Polystyrene is the currently preferred styrenic polymer and,when the styrenic polymer being brominated is a copolymer of two or morevinyl aromatic monomers, it is preferred that styrene be one of themonomers and that styrene comprise at least 50 weight percent of thecopolymerizable vinyl aromatic monomers.

The styrenic polymers, which are brominated in accordance with thepresent invention, are readily prepared by bulk or mass, solution,suspension or emulsion polymerization techniques comparable to thoseemployed in the polymerization of styrene. Polymerization can beeffected in the presence of free radical, cationic or anionicinitiators, such as di-t-butyl peroxide, azo-bis(isobutyronitrile),di-benzoyl peroxide, t-butyl perbenzoate, dicumyl peroxide, potassiumpersulfate, aluminum trichloride, boron trifluoride, etherate complexes,titanium tetrachloride, n-butyllithium, t-butyllithium, cumylpotassium,1,3-trilithiocyclohexane, and the like. The polymerization of styrene,alone or in the presence of one or more monomers copolymerizable withstyrene, is well known and it is considered unnecessary to furtherdiscuss the polymerization process. The styrenic polymers having amolecular weight of at least 1,000, preferably at least 50,000 and mostpreferably 150,000 to 500,000, are brominated in accordance with thepresent invention. Although styrenic polymers outside these molecularweight ranges can be brominated in accordance with the presentinvention, there is typically no economic advantage in so doing.

The catalyst used in the processes of this invention can be anybromination catalyst, provided that the catalyst does not act tofrustrate the efficient and safe production of a high quality brominatedpolystyrenic product. The favored catalysts are the Lewis acid catalystswhich are typified by AlCl₃, FeCl₃, AlBr₃, FeBr₃, SbCl₅, ZrCl₄, and thelike. Fe, Al and Sb₂ O₃ may be used to form Lewis acid catalysts bysimply adding them to the reaction system. Mixtures of catalyst can alsobe used. Once the catalyst has been added to the reaction system, it mayundergo some reaction without significant loss of catalytic activity,e.g., AlCl₃ may convert to some extent to AlBr₃. The more preferredcatalysts are the aluminum and iron-based catalysts. Of these, the mostpreferred are the aluminum and iron halides, especially the bromides andchlorides. AlCl₃ and FeCl₃ are most highly preferred, with AlCl₃ beingthe catalyst of choice.

The catalyst is used in an amount which is sufficient to obtain thecatalytic effect sought. These catalytic amounts will depend on theactivity of the catalyst, but will generally fall within the range offrom about 0.2 to about 20 weight percent and preferably within therange of from about 0.2 to about 15 weight percent, based on the weightof the styrenic polymer being brominated. The most active catalysts willbe used in the lower amounts while the less active catalysts will beused in the higher amounts. For the preferred aluminum and iron-basedcatalysts, it is preferred that they be used in amounts within the rangeof from about 0.5 to about 5 weight percent. AlCl₃ and FeCl₃ are usefulin amounts within the range of from about 0.5 to about 10 weightpercent. When AlCl₃ is the catalyst, amounts within the range of fromabout 0.5 to about 3 weight percent are preferred.

The brominating agents useful in the processes of this invention can beany of those which can brominate aromatic carbons in the polymer's vinylaromatic units (hereinafter also referred to as styrenic monomer units).The art recognizes Br₂ and BrCl as good brominating agents, with theformer being most preferred. Bromine can be obtained commercially in thediatomic form or can be generated by the oxidation of HBr. Br₂ can besupplied either as a liquid or a gas. The amount of brominating agentused in the process should provide an overall mole ratio of totalbrominating agent to total styrenic polymer fed, which will provide from1 to 3 bromine substitutions per styrenic monomer unit in the polymer.Generally, it is desired that the brominated styrenic polymer productsof this invention contain at least 30 wt % bromine, based upon the totalweight of the brominated polymer. It is preferred that the brominatedpolymer contain above about 50 wt % bromine and most preferably aboveabout 60 wt % bromine. For any particular styrenic polymer, the amountof brominating agent used in the process will be determined by thebromine content desired considering the highest bromine content which isobtainable with the process parameters chosen. The higher brominecontents will require the most brominating agent. It is pointed out thatas perbromination is approached, it becomes more difficult to substitutethe last bromines. Adding ever larger amounts of a brominating agentdoes not always attenuate this difficulty. However, it is helpful, inattempting to maximize the bromine content, to provide a smallstoichiometric excess of brominating agent. Stoichiometric excesses upto about 10% are preferred. The stoichiometry is easily determined as itrequires one mole of Br₂ or BrCl per substitution sought. In practice,the practitioner will determine the bromine content sought on a weightbasis and then will calculate, on an idealized basis, the number ofmoles of brominating agent needed to obtain the same. For example, ifthe styrenic polymer is polystyrene and the bromine content sought is 68wt %, at least 2.7 moles of bromine or BrCl per styrenic monomer unitwill be required, not including any desired stoichiometric excess. Forbrominated polystyrene, a bromine content of from about 40 to about 70+wt % bromine is desirable. This range can be theoretically obtained witha mole ratio of bromine to styrenic monomer unit of from about 0.9:1 toabout 3.0:1 Preferred for brominated polystyrene is a bromine content offrom about 60 to about 70+ wt %, which can be obtained with atheoretical mole ratio of from about 1.9:1 to about 3.0:1 for bromine orBrCl. The processes of this invention can, with facility, provide up to70 wt %, say 67-68 wt %, bromine. For addition modes (2) and (3), theamount of brominating agent used in the process is that amount ofbrominating agent in the feed mixture and any brominating agentpre-added to the catalyst. As pointed out herein, for addition mode (3),it is not necessary to pre-add a brominating agent to the catalyst and,thus, all of the process brominating agent requirements can be suppliedvia the feed of the mixture. If, however, the practitioner chooses topre-add a brominating agent to the reactor, it can be done and thatamount of brominating agent is part of the overall amount of brominatingagent used.

While the foregoing describes the overall quantitative relationshipbetween the brominating agent and styrenic polymer, the quantitativerelationship between these two reactants in the feed mixture foraddition mode (3) has not been fully discussed. Generally, the mixturewhich is to be fed will contain from about 1 to about 8 moles ofbrominating agent per mole of styrenic monomer units at any time duringthe feed period. During the feed, the quantitative relationship can beconstant or can vary within the above-mentioned range. (It is within thescope of this invention to allow for some excursions outside of therange so long as such does not do significant harm to the processefficiency or to product quality.) A preferred range is from about 2.5to about 5 moles of brominating agent per mole of styrenic monomer unitsin the feed mixture. As can be appreciated, the use of an amount ofbrominating agent in the feed mixture which gives a mole ratio ofbrominating agent to styrenic monomer units which is less than orgreater than the selected overall mole ratio of brominating agent tostyrenic monomer units, will result in exhaustion of either thebrominating agent or the styrenic polymer as a mixture constituentbefore exhaustion of the other constituent. For example, if thepractitioner chooses to produce brominated polystyrene with a 70 wt %bromine content, an overall molar ratio of bromine to styrenic monomerunits of 3.0:1, and any excess if desired, would be suitable. If thepractitioner chooses to form a feed mixture in which the molar ratio ofbromine to styrenic monomer units is 1:1, it can be seen that the amountof polystyrene to be fed will be completed before obtaining the neededoverall amount of bromine. In this case, the practitioner first uses the1:1 mixture and then continues on with just a bromine feed after thepolystyrene feed has been exhausted. If, on the other hand, the molarratio in the feed mixture is chosen to be 5:1, then the bromine willfirst become exhausted and the feed will have to be finished with thepolystyrene alone. Generally, it is preferred to have the overall molarratio and the feed mixture ratio at least somewhat similar. In all casesthough, the initial feed should preferably contain at least a molarratio of bromine to styrenic monomer units of 1:1.

It is preferred that the bromine used in the processes of this inventionbe essentially anhydrous, i.e., contain less than 100 ppm (weight basis)water and contain no more than 10 ppm organic impurities, e.g., oil,grease, carbonyl containing hydrocarbons, iron, and the like. Available,commercial grade bromine may have such purity. If, however, such is notavailable, the organic impurities and water content of the bromine canbe conveniently reduced by mixing together a 3 to 1 volume ratio ofbromine and concentrated (94-98 percent) sulfuric acid. A two-phase mixis formed which is stirred for 10-16 hours. After stirring and settling,the sulfuric acid phase, along with the impurities and water, isseparated from the bromine phase. To further enhance the purity of thebromine, the recovered bromine phase can be subjected to distillation.

By forming a solution of bromochloromethane and styrenic polymer, thepolymer becomes easy to handle and mix with bromine. The solutions ofthis invention, e.g., the reactor contents for addition mode (1) and thepolystyrene streams for addition modes (2) and (3), will generallycontain from about 5 to about 50 wt % polymer. More highly preferred arethose which contain from about 5 to about 30 wt % polymer. Whenconsidering the total bromochloromethane in the process, which totalwould include that amount of bromochloromethane used to render thecatalyst stirrable in addition modes (2) and (3), typically there willbe 5 to 40 wt % styrenic polymer. Preferably, this range will have anupper limit of from 20 to 35 wt % styrenic polymer, the wt % being basedon the total weight of bromochloromethane and styrenic polymer used inthe process.

It is preferred to have the bromination catalyst associated with anamount of bromochloromethane so that the catalyst can be in a solution,slurry, dispersion or suspension as it is being contacted with thebrominating agent and styrenic polymer. Such will enhance reaction massmixing and mass transfer qualities. This association is best whenconsidered to be a suspension. It is suitable to use from about 95 toabout 99.9 wt % bromochloromethane and preferably from about 99 to about99.8 wt %, based on the total weight of bromochloromethane and catalyst.

The feeds used in the processes of this invention should occurexpeditiously, with consideration being given to the ability of theprocess equipment to handle the heat load from the exothermic process,the evolving HBr, and other process concerns. In short, the feeds canoccur over the shortest time period that will be allowed by theequipment without excursion outside of critical process parameters.Generally, it is anticipated that the feed period will be from 0.5 to 3hours for a commercial-size plant. Shorter feed periods are expected forsmaller scale processes.

The processes of this invention occur at a temperature within the rangeof from about -20° to about 60° C. and preferably within the range offrom about 0° to about 10° C. The pressure can be atmospheric,subatmospheric or superatmospheric.

To carry out a process of this invention, a bromination catalyst, sayAlCl₃, is suspended in essentially anhydrous bromochloromethane, to givean easily stirrable suspension. The suspension is prepared in aglass-lined, stirred reactor and brought to a temperature within therange of from about -5° to about 10° C. The mix is kept under an inert,dry atmosphere in the reactor. A solution of a styrenic polymer andbromochloromethane is prepared and intimately mixed with a brominestream to yield a homogenous mixture. The cool mixture is fed into thestirred bromination catalyst suspension in the reactor. The intimatemixing of the styrenic polymer solution and brominating agent can beaccomplished in a number of ways. For example, the solution and abrominating agent can be fed to a mixing device, e.g., a mixing nozzle,at the lower end of the dip tube in the reactor which extends to a pointbelow the suspension level. The mixing device is designed to obtain theintimate mixing of the solution and brominating agent. Also, the mixingdevice acts to impart mixing energy, at the point of feed, to theintimate mixture and catalyst suspension. Another technique forobtaining intimate mixing of the styrenic polymer solution andbrominating agent, is to use an exterior reactor loop having an in-linemixer, say an impingement mixer. Generally, the use of an exteriorreactor loop includes first charging the reactor with a brominationcatalyst slurry, suspension, etc., and then withdrawing from the reactora stream which is then fed to a mixer external of the reactor. A mixtureformed from at least bromine and styrenic polymer is also fed to themixer to yield a second mixture which is formed from the two feeds tothe mixer. The second mixture is subsequently fed back to the reactor.The stream withdrawn from the reactor will initially comprise thecatalyst. After the second mixture is fed to the reactor and the processruns, the withdrawn stream will begin to comprise brominated polystyrenealong with catalyst. As the process continues, the degree of brominationof the polystyrene will increase.

Exemplifying the use of an exterior reactor loop, reference is made toFIG. 1 wherein there is shown a reactor, generally designated by thenumeral 1. Reactor 1 is a stirred reactor and initially contains asuspension comprising catalyst and bromochloromethane. Reactor dischargeconduit 4 provides a stream from reactor 1 which is fed to pump 5. Pump5 pressurizes the stream so that it is fed with force via conduit 7 toimpingement mixer 10. Bromine is fed via conduit 20 to pump P₁ while, atthe same time, a solution of polystyrene and bromochloromethane is fedvia conduit 22 to pump P₂. Pumps P₁ and P₂ feed in-line mixer 11 toobtain an intimate mixture of bromine, polystyrene, andbromochloromethane solvent. This intimate mixture is fed to impingementmixer 10, wherein it is intimately mixed with the stream from reactor 1.The discharge from impingement mixer 10 is fed via conduit 33 to reactor1 through feed port 3. The removal of contents from reactor 1 and theirfeed to impingement mixer 10 continues to occur until at leastsubstantially all of the bromine and polystyrene/bromochloromethanesolution have been fed.

As can be appreciated, the contents of reactor 1 change in compositionduring the bromine and polystyrene/bromochloromethane solution feeds.Initially, the contents of reactor 1 comprise catalyst andbromochloromethane. As the process runs, the reactor contents compriseand begin to become more rich in brominated polystyrene, some of whichis underbrominated and some of which is of the degree of brominationsought. During a cook period, the final bromination occurs. Removal ofthe reactor contents can continue to occur during the cook period to aidin mixing.

As pointed out earlier, the bromination of styrenic polymers is asubstitution reaction. The main by-product from this reaction is HBr.The HBr formed in the process is usually found in the head space abovethe reactor contents. It is preferred that the HBr be removed and passedto a water scrubber or stored as dry HBr. A dry, inert gas, saynitrogen, can be used as a pad over the reactor contents to minimize thepresence of water therein.

The reactor is kept at a low temperature, e.g., from about 0° to about10° C., during the feed of styrenic polymer and/or brominating agentfeed, as the case may be, and preferably from about 4° to about 8° C.

After the feed is accomplished, the reactor is preferably maintained fora cook period of from about 0.5 to about 6 hours and preferably fromabout 1 to about 3 hours. The cook temperature is within the range offrom about 0° to about 10° C. and preferably within the range of fromabout 2° to about 5° C. The cook period serves to continue thebromination until the sought degree of bromination is obtained. It maybe for a long period if the reaction parameters provide for mildbromination conditions during the brominating agent and styrenic polymerfeeds or it may be for a short period if the parameters chosen providefor more severe bromination conditions. The cook period can occur in thereactor.

After the cook period, the reaction mass can be treated with water,sodium sulfite, sodium gluconate and sodium hydroxide to deactivate thecatalyst, kill any remaining brominating agent and to adjust thereaction mass pH. After these treatments, the reaction mass is settledto obtain a two-phase reaction mass containing an organic phase, whichcontains, as a solute, the brominated styrenic polymer product, and anaqueous phase. The aqueous phase is decanted and the remaining organicphase is stripped of its bromochloromethane component. It is mostconvenient to accomplish this strip by pouring the organic phase intoboiling water. As the solvent is stripped, the brominated styrenicpolymer product forms a precipitate. The precipitate can be recovered byany liquid-solid separation technique, e.g., filtration, centrifugation,etc. The recovered precipitate is then dried.

It is preferred that the bromochloromethane solvent be dry, that is itcontains less than about 200 ppm (weight basis) water and morepreferably less than about 150 or 100 ppm water.

The following Examples illustrate features of processes of thisinvention. The Delta E values, along with the L, a and b values fromwhich it is derived, were obtained by transmission measurements madewith a HunterLab Color Quest Spectrocolorimeter. The transmission cellprovided a 20 mm path length. The software was set to report the colorin units of "Delta E-lab". The standardization/calibration was basedupon chlorobenzene and obtained by use of the instrument's black andwhite standard tiles. The brominated polystyrene sample to be tested wasprepared by measuring 5 grams of the sample into a 50 ml centrifugetube. Then, 45 grams of chlorobenzene was placed in the tube. The tubeis shaken for 1 hour on a wrist-action shaker. If, after the shakingperiod has lapsed, the solution is not clear it is centrifuged for 10minutes, at 4,000 rpm. If the solution is still not clear, it is thencentrifuged another 10 minutes. If the solution is still not clear, thenit cannot be analyzed. Assuming a clear solution, the solution is pouredto fill the 20 mm cell for placement in the colorimeter. The calibratedinstrument is set to report color as "Delta E-lab".

EXAMPLE I Batch Bromination of Polystyrene Bromochloromethane Solvent

Bromine (683.5 g, 4.277 mole) was added over 75 minutes to a cooled (5°C.) solution of 165.0 g (1.585 mole) of polystyrene (PS) dissolved in1,188 ml (2,364 g) of anhydrous bromochloromethane (BCM) in the presenceof 3.3 g (2.9 wt % based on PS) of aluminum chloride. Evolved HBr wasscrubbed by a caustic solution during the reaction. A cook period of 2hours at 5° C. with nitrogen purge was effected. The reactor contentswere diluted with 2,444 ml (4,863 g) BCM, washed with 2,000 ml water,aqueous sodium sulfite (30 g in 2,000 ml water) and then with 2,000 mlwater. The aqueous and organic layers were separated. The organic layerwas added batchwise into 7,000 ml of 90° C. water with agitation. BCMwas removed with a Dean-Stark trap from the return distillate. Themixture was cooled and the solid product was filtered, washed (withwater) and dried at 150° C. to obtain 477 g (95% yield) of brominatedPS. The results of analysis are shown in the Table.

EXAMPLE II Batch Bromination of Polystyrene Ethylene Dichloride Solvent

The bromination of PS was repeated as in Example I except as indicatedin the Table. The amount of ethylene dichloride, EDC, used was in thesame volume proportion as the BCM used in each step. The analyticalresults for the product are in the Table.

EXAMPLE III Pre-mix of Polystyrene and Bromine for the Bromination ofPolystyrene Bromochloromethane Solvent

A Y-shaped mixing apparatus having a cooling jacket was equipped with 2feed lines, each connected to a pump. One of the feed lines was fordelivering bromine and the other was for delivering a PS and BCMsolution. Bromine (93.3 g, 31.3 ml or 0.583 mole), delivered at a rateof 1 ml/min (19.4 mmol/min), and a PS/BCM solution (22.4 g PS, 0.215mole and 97 ml or 194 g of anhydrous BCM), delivered at 4 ml/min (7.17mmol/min), were fed simultaneously from their respective feed lines intothe cooled (5° C.) Y-mixing apparatus. The resultant intimate mixturefrom the mixing apparatus was then fed into a cooled (5° C.) suspensionof 0.45 g (2 wt % based on PS) of aluminum chloride in 49 ml (98 g) ofanhydrous BCM. Evolved HBr was scrubbed by a caustic solution during thereaction. The feeds were complete in 35 minutes and the mixture wascooked for 2 hours at 5° C. After water and sodium sulfite washes, solidBrPS was isolated by precipitating from 500 ml of hot (90° C.) water asdescribed above. A total of 66 g of BrPS (97%, yield) was obtained. Theresults of analysis are shown in the Table.

EXAMPLE IV Pre-mix of Polystyrene and Bromine for the Bromination ofPolystyrene Ethylene Dichloride Solvent

The bromination of PS was repeated as in Example III except as indicatedin the Table. The amount of EDC used was the same volume proportion asthe BCM used in each step. The analytical results are in the Table.

EXAMPLE V Co-feed of Separate Streams of Polystyrene and Bromine for theBromination of Polystyrene Bromochloromethane Solvent

Aluminum chloride (3.54 g, 2 wt % based on PS) was suspended in 379 ml(754 g) of anhydrous BCM. After cooling to 3° C., a 10-ml portion ofbromine was added. A solution of PS/BCM (175 g or 1.681 mole of PSdissolved in 791 ml or 1,574 g of anhydrous BCM) was pumped into thesuspension at a rate of 15 ml/min (25.47 mmol/min), while bromine (totalof 725 g, 230 ml, 4.537 moles, 2.7 equivalents) was added from anaddition funnel at a rate of 3 ml/min (58 mmol/min). Evolved HBr wasscrubbed by a caustic solution during the reaction. The mixture was heldat 5° C. throughout the feed and cook period. After 3.3-hr cook, themixture was diluted with BCM (1,068 ml or 2,127 g) and then washed withaqueous sodium sulfite and water. The product was precipitated in waterand isolated as described in the previous section. A total of 522 g ofBrPS (98% yield) was obtained. The results of analysis are shown in theTable.

EXAMPLE VI Co-feed of Separate Streams of Polystyrene and Bromine forthe Bromination of Polystyrene Ethylene Dichloride Solvent

The bromination of PS was repeated as in Example V except as isindicated in the Table. The amount of EDC used was in the same volumeproportion as the BCM used in each step. The analytical results are inthe Table.

                                      TABLE                                       __________________________________________________________________________                    Ex. I Ex. II                                                                              Ex. III                                                                             Ex. IV                                                                              Ex. V Ex. VI                          __________________________________________________________________________    Mode of Addition                                                                              Batch Batch Premixed                                                                            Premixed                                                                            Cofeed                                                                              Cofeed                          Solvent/deg C.  BCM/5 EDC/5 BCM/5 EDC/5 BCM/5 EDC/5                           AlCl3 Load (wt % of PS)                                                                       2     2.7   2     2.1   2     2                               Avg Feed Mole Ratio Br/PS                                                                     --    --    2.7   2.7   2.3   2.2                             Total Eq. Br2   2.7   2.8   2.7   2.7   2.7   2.7                             Feed Times Br2/PS (min/min)                                                                   75/0  67/0  35/35 30/30 76/66 76/62                           Cook Time (min) 240   140   120   120   200   200                             BrPS Yield (%)  95          97    97    98    97                              Total Br (wt %) 66.8  68.2  68.4  67.6  68.0  67.0                            Hydro. Br (ppm) 2,868 7,138 2,827 3,778 1,695 2,680                           Solution Color (10% PhCl)                                                     L               93.21 88.97 96.74 87.10 96.94 96.45                           a               -2.86 -3.34 -1.90 -1.68 -1.12 -2.51                           b               22.24 36.65 15.99 34.80 7.89  13.80                           Delta E         23.43 38.42 16.44 37.15 8.54  14.48                           GC Analysis of Solvent (Area %)                                               Before Reaction 99.44 99.97 99.44 99.97 99.44 99.97                           After Reaction  99.49 99.70 99.28 99.06 99.35 98.64                           New Impurities in Recov. Solvent                                              Ethylene Dibromide                                                                            --    0.18  --    0.90  --    1.28                            Dibromobenzene  0.02  0.10  --    --    --    --                              __________________________________________________________________________

As can be seen from the Table, the use of bromochloromethane provides abrominate product having superior color and Delta E values with littleor no degradation of the process solvent.

EXAMPLE VII

A 0.910 g (6.82 mmol) portion of aluminum chloride was suspended(stirred at 250 rpm) in 190 g of dry (13 ppm water) bromochloromethane(BCM) in 1-L jacketed flask cooled to 0° C. by circulating glycol bath.A 419.86 g portion of a 10.00 wt % solution of polystyrene (403.1/nmmol) in dry B CM was pumped at a constant rate of 8.46 g/min (8.13mmol/min) to a jacketed, glycol-cooled mixing tee mounted on thereaction flask. At the same time, bromine was pumped at a constant rateof 6.09 g/min (38.1 mmol/min) to the same mixing tee where it combinedwith the polystyrene solution (feed mol ratio Br₂ /PS is 4.69) beforedropping into the stirred catalyst suspension in the reaction flask. Thebromine feed was stopped after 30.0 min (1143.5 mmol) and thepolystyrene solution feed was stopped after 49.6 min (overall mol ratioof Br₂ /PS is 2.84). A rinse of 160 g of dry BCM was used for thepolystyrene solution feed system to assure complete transfer of thepolymer to the reaction flask. The reaction temperature was maintainedat 0°-5° C. throughout the addition and subsequent 2 hr cook period. Thecatalyst was deactivated by addition of 16.4 g of 10 wt % aqueoussolution of sodium gluconate, and pH was adjusted to 14 by addition of60.7 g of 10 wt % aqueous NaOH. The reaction mixture was washed with 10wt % aqueous sodium sulfite followed by a water wash. The product wasrecovered from the organic phase by addition to vigorously stirred hot(90° C.) water. The solvent distilled from the hot water leaving aslurry of the brominated polystyrene product in water. After filtering,the powdery solid was rinsed with water and dried to constant weight ina vacuum oven (150° C./2 torr/5 hr). The dry solid weighed 127.08 g (95%yield). The product contained 68.7 wt % total Br and 3600 ppmhydrolyzable Br. The HunterLab solution color (10 wt % in chlorobenzene)values were L=94.58, a=-2.79, b=17.29 Delta E=18.34.

The brominated styrenic polymers of this invention are suitable for useas flame retardants in thermoplastics, especially engineeringthermoplastics, e.g., polybutylene terephthalate, polyethyleneterephthalate, nylon and the like. These brominated polymers are used inflame retarding quantities, say from about 5 to about 20 wt % brominatedpolymer per hundred weight of thermoplastic. Conventional blendingtechniques can be used as taught in the prior art. In addition,conventional additives, such as UV stabilizers, impact modifiers, flameretardant synergists, dyes, pigments, fillers, plasticizers, flow aids,antioxidants, free radical initiators, and the like may be used as theneed requires.

What is claimed:
 1. A process which comprises contacting styrenicpolymer with a brominating agent in the presence of Lewis acid catalystand solvent quantities of bromochloromethane.
 2. The process of claim 1wherein the brominating agent is bromine, bromine chloride or a mixturethereof.
 3. The process of claim 1 wherein the styrenic polymer ispolystyrene.
 4. The process of claim 1 wherein the Lewis acid catalystis aluminum halide.
 5. The process of claim 1 wherein the Lewis acidcatalyst is AlCl₃, AlBr₃ or a mixture thereof.
 6. The process of claim 1wherein the brominating agent is bromine, bromine chloride or a mixturethereof, the styrenic polymer is polystyrene and the Lewis acid catalystis AlCl₃, AlBr₃ or a mixture thereof.